A neutron star centered in a disk of hot plasma drawn from its red companion star. Accreting material from the disk, the neutron star spins faster and faster emitting powerful particle beams and pulses of X-rays as it rotates 400 times a sec. Credit: W. Feimer (Allied Signal), GSFC, NASA.
An X-ray pulsar is an X-ray binary in which the compact object is a neutron star with a powerful magnetic field that gives rise to regular X-ray pulses. These pulses are thought to be caused by the magnetic field channeling the accreting gas on to the poles of the compact star, producing localized hot spots that move in and out of view as the star spins. Hercules X-1 is an example. Anomalous X-ray pulsars (AXPs) make up an unusual subcategory.